Image guided medical and surgical procedures utilize patient images obtained prior to or during a medical procedure to guide a physician performing the procedure. Recent advances in imaging technology, especially in imaging technologies that produce highly-detailed, computer-generated two, three and four-dimensional images, such as computed tomography (CT), magnetic resonance imaging (MRI), isocentric C-arm fluoroscopic imaging, fluoroscopes or ultrasounds have increased the interest in image guided medical procedures. During these image guided medical procedures, the area of interest of the patient that has been imaged is displayed on a display. Surgical instruments and/or implants that are used during the medical procedure are tracked and superimposed onto the display to show the location of the surgical instrument relative to the area of interest in the body.
A example of an image guided surgical navigation system that enables the physician to see the location of an instrument relative to a patient's anatomy, without the need to acquire real-time fluoroscopic images throughout the surgical procedure is generally disclosed in U.S. Pat. No. 6,470,207, entitled “Navigational Guidance Via Computer-Assisted Fluoroscopic Imaging,” issued Oct. 22, 2002, which is incorporated herein by reference in its entirety. In this system, representations of surgical instruments are overlaid on pre-acquired fluoroscopic images of a patient based on the position of the instruments determined by a tracking sensor.
Before overlaying a three-dimensional image with graphical representations of surgical instruments, the corresponding points in the three-dimensional image and points in the patient's reference frame must be determined. This procedure is generally known as registration of the image. A representative system that performs image registration is set out in U.S. Pat. No. 6,470,207. The three-dimensional patient specific images can be registered to a patient on the operating room table (surgical space) using multiple two-dimensional image projections. This process is often referred to as 2D/3D registration, which uses spatial transformations that can be established. This transformation is generally between the acquired fluoroscopic images and the three-dimensional image data set, such as CT or MRI images corresponding to the same patient. Once the transformations have been established, it is possible to directly relate the surgical space to both the two-dimensional and three-dimensional image space.
Various ways of achieving 2D to 3D registration by utilizing acquired 2D images to register 3D volume images are known in the art. These types of 2D to 3D registrations include contour algorithms, point registration algorithms, surface registration algorithms, density comparison algorithms, and pattern intensity registration algorithms. These registrations, however, are very computationally tasking and therefore, generally take several minutes to perform the 2D to 3D registration. In fact, some of these registrations can take upwards of twenty minutes to an hour to perform the registration. Moreover, these registration processes may also result in an inaccurate registration after waiting an extensive period of time.
It is, therefore, desirable to provide a method and apparatus for performing 2D to 3D registration in a more accurate and efficient manner, which does not suffer from the above-mentioned disadvantages. It is, therefore, an object of the present invention to provide such a method and apparatus for performing 2D to 3D registration.